The present invention relates in general to leak detectors, and in particular to a new and useful system for detecting leaks along a pipeline, on a continuous and reliable basis.
Transport systems for hazardous gases are prone to leaks that can create dangerous situations in a very short time. Currently, available methods for continuously monitoring gas-carrying, buried pipelines are limited to detection of relatively large leaks. There is a great need for a system that can reliably detect smaller leaks and still be economical to implement and use.
Small leaks from underground gas-transport pipelines can cause pressure drops that are too small for existing systems to detect. However, a small leak can quickly generate a gas cloud. If such a cloud is ignited, an explosion that can cause a great deal of damage will result. Such pipelines can also run close to or right under populated areas and even a small explosion can cause sever property damage and loss of life. The early detection of small leaks is, therefore, very important so that appropriate action can be taken to avoid a catastrophe.
Continuous leak monitoring of long pipelines is not a simple task. Leaks can be detected in two general ways. The first is by detecting the substance that escapes the pipe, the second is by detecting certain leak-related properties such as pressure drops, acoustic emissions, volume balance changes and temperature changes.
In order for the first method to succeed, a sensor that detects the leaking substance has to be in physical contact with this substance and, therefore, has to be in close proximity to the leak. This requires a dense concentration of sensors and, thus for a long pipeline, will yield a large number of remote units and high costs. One such method uses a monitoring vehicle to drive above a buried pipeline, checking for the presence of escaping substance. The disadvantage of this method is that it is not a continuous monitoring system and, thus, a leak occurring between trips can release a large amount of gas before it is detected. Another system uses an underground cable, buried just above the pipeline, that is sensitive to the substance in the pipe. When a leak occurs, the part of the cable that is exposed to the leaking material changes in some property that is detectable from the monitoring station. Such cables tend to be costly, especially for long pipelines, not only in initial investment, but also in maintenance. Furthermore, the cables that are currently available are sensitive only to petroleum products.
The second general method identified above, uses indirect ways to detect the presence of a leak. Temperature monitoring and volume balance comparison (comparing the amount of material injected into the pipe to the amount received from the pipe) techniques are useful for the detection of large, catastrophic leaks, and are widely used today. These systems, however, are not sensitive to small leaks. There are several systems available today that detect leaks by acoustic emissions using a portable device that listens to the sound of the leak in the air. Again, the disadvantage of such a device is its inability to constantly monitor the full length of longer pipelines. See R. C. McMaster, Editor, Non Destructive Testing Handbookl, Vol. 1: "Leak Testing". Am. Soc, Of Metals, 1982.